The overall goal of this Small Business Innovation Research (SBIR) Phase II grant is to develop and validate a new instrument to measure and correct for the background isotope levels of 18O and 2H during DLW analysis by measuring the 17O stable isotope of oxygen in body water. This approach will address the two major limitations addressed above. First, by using 17O measurements to correct for background fluctuations in 18O and 2H, this approach will reduce the amount of 18O, and thus cost, of performing DLW studies. Results from our Phase I studies (see Preliminary Data below) show that background fluctuations in 18O and 17O in body water are correlated with an R2 of 0.96, background fluctuations in 2H and 17O are correlated with an R2 of 0.89, and background fluctuations in 2H and 18O are correlated with an R2 of 0.92. Based on these correlations, using 17O measurements to estimate the background fluctuations of the 2H and 18O will provide an estimated forty percent decrease in the uncertainty of the DLW method due to background fluctuation. Second, The proposed instrument will be utilized in the new, triple-isotope method for DLW which will reduce existing barriers to widespread use of the DLW method by improving precision, reducing costs, reducing the technical expertise required to perform the analysis, and increasing throughput. Development of the new instrument will be performed by our business partners, Los Gatos Research, and validation studies will be performed at the University of Colorado Anschutz Medical campus.